1. Field of the Invention
The present invention relates to printheads of ink cartridges for ink jet printing and, more particularly, to a filter for an ink jet cartridge printhead.
2. Description of the Related Art
There are several types of electronic printers currently in wide-spread use. One type is known as the laser printer while another type is known as the ink jet printer.
The laser printer utilizes toner from a toner cartridge deposited onto the print medium to produce printing. The ink jet printer utilizes ink from an ink cartridge assembly to deposit or jet ink onto a print medium such as paper in a predetermined pattern from a plurality of ink emitting orifices or nozzles.
Generally, ink jet printers are thermal, drop on demand systems that utilize thermal energy pulses to produce vapor bubbles in ink-filled channels, each channel in communication with an orifice or nozzle. The vapor bubbles produced in the ink-filled chambers which are connected to channels cause the ink to be expelled from the orifices. The channels are in communication with an ink reservoir. Thermal energy generators, usually resistors, are located in the chambers near the nozzle. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble that expels an ink droplet toward the print medium. The printhead includes the plurality of nozzles in a predetermined pattern.
The printhead includes a heater chip and nozzle plate. The heater chip is conventionally formed with active semiconductor devices in silicon. The heater chip includes arrays of resistive and active elements oriented both horizontally and vertically which when mated with a nozzle plate forms a path for thermal ejection of ink drops. Depending upon the physical orientation of the nozzle plate relative to the print receiving medium, the diameter of the nozzles and the spacing between nozzles determines the vertical size of the print swath, and the horizontal width and spacing determine the packing density and firing rate of the printhead. As printing speeds and resolution density increase, larger and larger arrays of smaller elements and smaller diameter nozzles are utilized.
Ink jet printers currently on the market generally have a resolution of 300 to 360 dpi (dots per inch). Ink jet printers with higher resolutions currently may reach 720 dpi or higher. As can be appreciated, printing at 720 dpi has approximately four times the resolution as 360 dpi. In other words, at 720 dpi a one inch square printing area contains 720.times.720 or 518,400 dots. A resolution of 360 dpi, on the other hand, has a 360.times.360 or 129,600 dots per one inch square printing area. The resolution depends at least in part on the configuration of the printhead. Because the number of nozzles must increase for higher dpi printing resolutions, the size or diameter of each nozzle must necessarily decrease in order to maintain the same size printhead.
Since the nozzle diameters are relatively small, mechanical filters are used to remove particles from the ink in ink jet print cartridges that if not filtered would tend to cause clogs in the nozzles. These mechanical filters are generally screen mesh filters disposed over what is known as a standpipe. The standpipe provides fluid communication between the ink supply and the printhead.
It is now conceivable for ink jet printers to have resolutions of 1200 dpi. Because of the small diameter nozzles necessary to achieve 1200 dpi, it will become essential to filter smaller particles from the ink with a smaller pressure drop. If filtration is inadequate, the resulting clogged nozzles will eventually lead to a failed printhead. Also, inadequate filtration leads to bad or unsightly printing.
What is thus needed is an ink filter for ink jet printers that will provide filtration of minute particles with a small pressure drop.